It is often desirable to produce black-and-white photographic images formed by a combination of maximum density areas and minimum density areas. For such imaging applications a contrast of at least 10 (herein referred to as high contrast) and more typically near or above 20 is employed. An example of high contrast photographic elements having white reflective supports are phototypesetting materials intended to produce black type character images on a white background. An example of high contrast photographic elements having transparent supports are lith films, so called because they are used as contact transparencies for exposing lithographic printing plates. The illusion that some areas of a printed image are of intermediate density is created by the viewer's inability to resolve tiny dots of maximum density and background areas of minimum density that separate them. Such images are referred to as halftone images.
The use of hydrazines in negative working surface latent image forming silver halide emulsions and photographic elements to increase speed and contrast is taught by the following patent:
R-1: Trivelli et al U.S. Pat. No. 2,419,975. Increased contrast attributable to hydrazines in negative working surface latent image forming silver halide emulsions is believed to result from the promotion of infectious development. The hydrazines preferred for their higher effectiveness in increasing contrast are arylhydrazides. The acyl moiety of arylhydrazides increases activity while the aryl moiety acts to increase stability. A patent literature summary of arylhydrazides employed to increase contrast in negative working silver halide emulsions, including a discussion of the mechanism of activity, is provided by the following publication:
R-2: Research Disclosure, Vol. 235, November 1983, Item 23510. Research Disclosure is published by Kenneth Mason Publications, Ltd., Emsworth, Hampshire P010 7DD, England.
In surface latent image forming silver halide emulsions the grains which are exposed to light are rendered developable while grains which are not exposed to light are not intended to be developed. Nevertheless, some of these unexposed grains develop spontaneously. In fulltone imaging the spontaneously developing grains raise minimum density more or less uniformly. Such minimum density levels are referred to as fog and, so long as they remain low, are not objectionable.
Pepper fog differs from ordinary fog in that it takes the form of small, maximum density areas randomly distributed on a substantially uniform minimum density background. When a photographic element exhibiting pepper fog is viewed under magnification, the impression to the viewer is often that the magnified field of view has been sprinkled with grains of pepper. It has been long recognized that arylhydrazides produce pepper fog, and, until recently, this has interfered with the commercial use of arylhydrazides in halftone imaging. An illustration of severe pepper fog appears in FIG. 1.
Reduction of pepper fog as well as improved halftone imaging by employing an arylhydrazide that is substituted at its aryl moiety by an oxycarbamido, thiocarbamido, carbamoyloxy, or carbamoylthio group is disclosed in the following patent:
R-3: Loblaw et al U.S. Pat. No. 4,560,638. The incorporation of developing agents, such as hydroquinones, is also taught by R-3.
Thiazoline-2-thiones are known to be useful in photographic materials. Thiazoline-2-thiones which are N-substituted to prevent enolization are taught to be useful antifoggants, as illustrated by the following patent:
R-4: Rauch et al U.S. Pat. No. 3,081,170. Thiazoline-2-thiones which are N-substituted to prevent enolization are taught to be useful antifoggants in negative working photographic elements employing an arylhydrazide to achieve high contrast, as illustrated by the following patent:
R-5: Mifune et al U.S. Pat. No. 4,272,606. Carboxyalkyl-3H-thiazoline-2-thiones are disclosed to be useful antifoggants in dye enhanced photothermographic imaging systems, as illustrated by the following patent:
R-6: Shiao U.S. Pat. No. 4,138,265. Carboxyalkyl-3H-thiazoline-2-thiones are also disclosed to be useful in preserving color balance in multicolor photographic elements, as illustrated by the following patent:
R-7: Abbott et al U.S. Pat. No. 3,730,724.
R-8: James, The Theory of the Photographic Process, 4th Ed., Macmillan, Chapter 13, Section J. Antifoggants and Stabilizers, p. 396, states
Antifoggants or fog restrainers are agents that decrease the rate of fog density growth during development to a greater degree than they decrease the rate of image growth. Stabilizers are agents that decrease the changes in developable fog and/or in other sensitometric characteristics of the emulsion coating that occur during storage (aging). Some agents act in both capacities; others may act in only one capacity, or their action may be restricted to particular types of fog development or aging changes or both. Their quantitative, and sometimes their qualitative action depends upon the concentration as well as the chemical composition of the agents.
Thus, in assessing antifoggants and stabilizers it is important to note that stabilization and antifogging activity are sometimes both in evidence; however, stabilization and antifogging effects are independent and observations of utility for either purpose are valid only for the type of the photographic system employed. This is further illustrated by the following publication cataloguing a variety of known antifoggants and/or stabilizers, wherein the addenda and the photographic systems in which they are observed to be useful are correlated:
R-9: Research Disclosure, Vol. 176, December 1978, item 17643, Section VI.
Photographic elements employing an arylhydrazide to achieve high contrast have additionally had hydroquinone incorporated therein for varied purposes. The incorporation of hydroquinones in concentrations of from 5.times.10.sup.-2 to 5 mole/Ag mole to act as developing agents is taught in the following patent:
R-10: Takagi et al U.S. Pat. No. 4,385,108. The incorporation of indazole substituted hydroquinones to improve dot quality and screen range in halftone imaging is taught in the following patent:
R-11: Akimura et al U.S. Pat. No. 4,332,878. The incorporation of substituted hydroquinones, particularly thio group substituted hydroquinones, to improve speed and contrast and therefore halftone imaging characteristics, is disclosed by the following patent:
R-12: Mifune et al U.S. Pat. No. 4,377,634.
The use of carboxyalkyl-3H-thiazoline-2-thiones in high contrast arylhydrazide containing photographic elements to stabilize sensitivity is taught in the following patent application:
R-13: Cavallaro U.S. Ser. No. 756,157, filed concurrently herewith and commonly assigned, titled HIGH CONTRAST PHOTOGRAPHIC ELEMENTS EXHIBITING STABILIZED SENSITIVITY.
The use of polyhydroxybenzenes in high contrast arylhydrazide containing photographic elements to reduce pressure sensitivity is taught in the following patent application:
R-14: Loblaw U.S. Ser. No. 756,113, filed concurrently herewith and commonly assigned, titled HIGH CONTRAST PHOTOGRAPHIC ELEMENTS EXHIBITING REDUCED STRESS SENSITIVITY.